In a lumber grading process one method of determining the modulus of elasticity E, (Young's modulus) of a lumber specimen is to strike a starting end of said lumber specimen to produce a compressive stress wave in the lumber specimen which travels to the opposite end thereof and reflects from the opposite end as a tensile wave. The tensile wave travels back to the starting end, where it reflects as a compression wave, thus producing an echo reverberation. A measurement of the frequency of reverberations provides a measurement of sonic velocity. Alternative detection means can be used to detect the progress of the original compression wave whereby sonic velocity is determined, so time domain measurement of the first compression wave is interchangeable with measurement of reverberation frequency. The sonic velocity value is then combined with measured lumber specimen density. The result is a measured E value that can be used in a sorting process to grade structural lumber for characteristics that are important in the design and serviceability of a wood structure. Making the sonic velocity measurement requires a means for producing a compression/tension sonic wave in the lumber specimen under test. Such means have included pneumatic cylinders, pendulum devices, manually operated hammers and electric solenoid actuated hammers. One solenoid actuated hammer device utilized a commercial solenoid attached to a sliding shaft means the hardened end of which impinged upon a steel clamping means which in turn was attached to the lumber specimen whereby the sonic energy from the impact of the sliding shaft means was transferred to the lumber specimen. This arrangement was suitable for stop-and-go laboratory conditions but did not lend itself to a production line situation in which the sonic energy must be transferred into a continuously moving specimen.
The present invention provides a simple robust means for impacting the end of a moving lumber specimen, such as a lumber specimen riding on a conveyor chain, for the purpose of sonic lumber grading.